Yes, the 920 is a good watch, but it'll still set you back a couple of hundred on eBay in most cases! The barometric altimeter is now fried on mine (s/h on fleabay - worked for the first 18 months I had it), and this has been a common issue on 920 over the years. Garmin kit can be very glitchy in my experience.

Have you checked the altimeter hole is clear?

Oh yes, many times! When I recently changed the strap, I checked the hole that's in behind that too. I guess a hard/factory reset might help...although I doubt it.
_________________27 Years since it all began....

When my 910 went funny, Garmin customer support were able to take me into some of the engineer menus and some of the numbers from that proved the sensor itself was screwed, rather than it just outputting weird data due to being clogged up. Maybe worth the phonecall to get some certainty one way or another?
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Ok I haven't tested it yet in an actual Ironman, but the battery seems to last extremely well, I tend to forget to charge it more than anything as it always seems to just have life in it.

I would be very surprised if it didn't last a 13-14 hour IM Especially if you use a HR Strap

PS I got it last Black Friday for <£200 with a few HR Straps included, they are still sealed in the box as the wrist-based seems fine for most applications.

I've generally been really happy with my 735. I wear it pretty much all the time to record my swimming cycling and running and as a general activity tracker. My only complaint is in respect of battery life

The only IM I've used the watch for was Lanza this year. I turned off Glonas and made sure it was fully charged before the start. Everything was going well until about halfway into the run, when I got the low battery warning. The battery actually died at about 11:45 into the race . I was a bit disappointed given the manufacturer's claim of 13-14 hours. Does the use of a HR strap reduce battery usage? I've only ever used wrist-based HR with it because I find the straps irritate my skin over long runs.

Coincidentally, I met another Brit on the run course with the same watch. It turns out that his had died at about the same time in the race. He was also working on the basis that if he turned off as much as possible before the race then it should have lasted the course. He was mentally composing his letter to Garmin as he was shuffling along

This sample size is only N=2, but it certainly looks like there is an issue with battery life if you are planning on going over 11 hours for an IM.

In normal training usage I haven't had a problem with battery life. I just charge it every few days. Live track does seem to eat battery life - I reckon live tracking a bike ride with Glonas on will eat the battery in about 7 hours.
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I picked up a refurbed Fenix 3 a couple of years ago and have been pretty happy with it. Battery life is good, connects quickly to satellites, bluetooth to phone for alerts as well.

Only gripe would be the swim tracking, which seems quite a way off. I do have freakishly long arms though, so wondering if this is somehow throwing the open water tracking.
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Wrist-based HR is quoted to reduce battery life. But it doesn't actually say if using a strap helps or hinders or if they just mean no HR.

Optical will significantly reduce battery life. It must do. The emission of the lights in the sensors, and the processing power for the HR calculations based on the readings, will have to use some up.

I don't know that it's quantified anywhere, but connecting external sensors does use up some battery life. Simply because the watch is having to read that data and record it to the fit file. But a connected HR strap will consume nothing like the onboard optical functionality.
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Random stuff and race reports

As a mutli-sport watch, what are the meaningful differences between the 920 & 735? Can the 735 do all the power metrics and can you set-up Triathlon mode for timing events? Wrist-based HR is of no interest, can you turn that off?

ETA - looks like the trusty (haha) barometric altimeter is the only difference. How does the 735 give climbing data?
_________________27 Years since it all began....

Thanks everyone... I'm beginning to really like the look of the 735...

Battery life is a potential problem (my long-course time tends to be 15+ hours!) but it's a nice looking bit of kit and seems to be going for around late-£100's on fleabay...
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But 3 data fields fit really well onto the round design - either 1/2 + 2x 1/4 or stacked in 1/3s, with the middle line bigger. 3 fields seems to be how I configure most of my screens so it works well for me.

Then I went from the 910 to the 935, so the size and technology leap was substantial!